This invention relates in general to electrostatographic reproduction apparatus, and more particularly to a photoconductive image receiving member with optimized light response characteristics for an electrostatographic reproduction apparatus capable of both optical copying and nonimpact printing.
In reproduction apparatus, such as electrostatographic reproduction apparatus for example, it is general practice to provide an electrostatic image receiving member movable along a path relative to electrostatographic process stations. The electrostatic image receiving member may be in the form of a roller or web guided for movement along the path by support rollers. In the electrostatographic process stations, a uniform electrostatic charge is applied to the member and such charge is modified in an area of the member to form, in such area, a latent image charge pattern corresponding to information to be reproduced. The latent image charge pattern is then developed by applying pigmented marking particles to the member, and the developed image is then transferred to a final receiver member and fixed thereto by heat and/or pressure for example.
The mechanism by which modification of the uniform electrostatic charge pattern to form the latent image is accomplished is dependent upon the characteristics of the image receiving member. If the image receiving member is of the type having a photoconductive layer, charge modification is accomplished by exposing the member to light in an image-wise pattern. Exposing of a image receiving member having a photoconductive layer has typically been accomplished by one of two methods. One method of exposure involves forming a light image of a document (referred to generally as optical copying). In this method, light is directed from a lamp assembly at a document with the light reflected from (or transmitted through) the document being directed by a lens unit into focus on the photoconductive surface. The light from the lamp may illuminate the entire document at one time (referred to as flash exposure), or may be passed through a slit and moved relative to the document to illuminate successive line segments of the document (referred to as scan exposure).
The second method of exposure involves the use of an electronically controlled light emitting assembly (referred to generally as nonimpact printing). Examples of electronically controlled light emitting assemblies include lasers, electrooptic gating devices, or arrays of light emitting diodes (LED's). The light emitting element(s) of an electronically controlled light emitting assembly is selectively turned on and off to produce a beam (or individual beams) of light focused on the photoconductive surface of the image receiving member in order to expose the photoconductive surface in a line-by-line fashion. Information to be reproduced is electronically generated and is used to control the turning on and off of the light emitting assembly to form a desired charge pattern creating a latent image on the member corresponding in an image-wise configuration to the information to be reproduced.
Certain electrostatographic reproduction apparatus in use today employ both image formation with visible light and image formation with electronically controlled light emitting elements (i.e., such apparatus are capable of both optical copying and nonimpact printing). Visible light is, of course in the range of 4000-7700 angstroms. However, certain common electronically controlled light emitting elements are biased toward the infrared range (i.e., greater than 7000 angstroms). The response characteristics of photoconductive image receiving members are generally suitable for optimization in either the visible range or the infrared range, but not both. In order to provide response sensitivity over a range to cover both visible light exposure and infrared exposure, it has been suggested that a photoconductive member have multiple layers of different response characteristics (see for example U.S. Pat. No. 4,607,934 issued Aug. 26, 1986 in the names of Kohyama et al). Such multi-layer photoconductive member construction would, however, be difficult to fabricate and one layer may adversely effect the sensitivity of another layer such that the overall sensitivity of the photoconductive member is degraded over some particular wave length ranges.